The rather recent realization that many of the disturbances of penile erection have an organic basis, has focused attention on unresolved problems in basic knowledge of the neural and vascular events in normal erection. The complexity of penile erection underscores the need for correlative anatomical and functional studies in a well-characterized model. Changes in blood distribution in the penis during erection are not well-understood, nor is it certain how active (neuro-muscular and passive mechanisms contribute to erection. To evaluate sites in the penis important in regulating blood flow and to obtain comprehensive data on the vasculature of the corpora cavernosa penis and the corpus spongiosum. Scanning electron microscopy of vascular casts will be made of the penis in the fiaccid state and after stimulation of vasodilator nerves. Neurohistochemical studies of the autonomic innervation of the corpus sporgiosum will be performed to understand how this erectile body may contribute to penile erection. Doubt has been expressed that penile vasodilator nerves are cholinergic, therefore organ bath studies of penile smooth muscle will be used to determine how endogenous substances such as acetylcholine cause vasodilation. Newer cholinergic agonists and antagonists drugs will be used both in receptor autoradiographic studies and in organ bath preparations to evaluate pre- and postsynaptic effects of acetylcholine. Participation of the hypogastric nerve in penile erection is not understood, but it is clear that it may compensate for the main vasodilator pathway of sacral origin. Nerve stimulation and measurement of pressure in the penis will be used (1) to determine if the accessory vasodilator pathway cooperates with the sacral pathway in erection in the intact animal and (2) to follow over time and quantitate compensatory changes in the vasodilator pathway after nerve injury. The proposed studies are intended to provide fundamental information necessary for interpreting the mechanism of penile erection in the normal and pathological state.